Patients who are immobilized due to partial or complete paralysis, or are recuperating from major surgery or otherwise bedridden for extended periods of time, or passengers in vehicles or office workers immobilized in chairs are often unable to exercise or move sufficiently under their own power. In many cases this is problematic and can lead to complications such as thrombosis or bed sores, and disuse atrophy of joints and soft tissues. Most solutions to this problem involve changing pressure points exerted on the patient's body by the bed or couch on which they are supported. Mattresses having fluidized beds incorporated into the structure or inflatable/deflatable devices are common but these units typically involve complicated mechanisms and circuitry and are quite expensive. A propagating wave through a body support is a desirable alternative to these other solutions.
Several types of wave generating devices have been patented. U.S. Pat. No. 3,981,612 issued to Bunger et al is directed to a wave generating apparatus which uses a set of rollers mounted on a carriage that is driven along a set of rails. A flexible sheet is secured at the ends of a frame and as the carriage is driven along the rails the roller displaces the sheet upwardly so that a wave motion is produced along the sheet. This device is quite bulky and is only able to produce one displacement wave for only one set of rollers.
U.S. Pat. No. 4,915,584 issued to Kashubara discloses a device for converting fluid flow into mechanical motion using an airfoil movable within a vertical track. As air flows over the air foil the foil moves vertically up or down in the vertical track thereby transmitting movement to a set of crank arms thereby rotating an axle which is attached at the ends to the two crank arms.
U.S. Pat. No. 4,465,941 issued to Wilson et al is directed to a water engine for converting water flow into other types of mechanical energy. Water flowing toward one side of the device engages a set of butterfly valves and a wheeled carriage is pushed along the frame of the barrage.
U.S. Pat. No. 3,620,651 issued to Hufton discloses a fluid flow apparatus that may operate as a pump or motor. The device includes several flexible sheets driven in oscillatory motion by a bulky crank assembly.
U.S. Pat. No. 4,999,861 issued to Huang describes a therapeutic bed with a wave surface generated through two longitudinal shafts, a multitude of offset cams and a support mechanism.
A PCT patent application PCT/EP98/01276 issued to Nestle S. A. uses a method similar to Huang's wave bed in a peristaltic pump. A longitudinal shaft drives a number of cams that sequentially compress a tube in a wavelike manner.
U.S. Pat. No. 5,267,364 issued to Volk also describes a wave bed activated through inflation and deflation of air pockets.
Though the main complication of venous thrombosis is fatal pulmonary embolism (PE), there are other long-term complications that account for considerable suffering and health care costs. Post-thrombotic syndrome (PTS) is the most common and chronic of these. It is characterized by pain, swelling, varicose eczema and, at its most severe, venous ulceration of the affected limb, most often the calf. Venous hypertension and valvular incompetence are believed to be the main factors responsible for the development of PTS. In general, most cases of PTS manifest within 2 years of acute deep vein thrombosis (DVT) with a cumulative incidence of 17 to 50%.
PTS is responsible for considerable personal disability, reduced quality of life and increased health care costs. Despite this, available therapies including graduated pressure stockings (GCS) and pneumatic compression pumps, placed over the calf, have major clinical limitations. Although pneumatic sequential compression pumps exact symptomatic relief in most subjects who use them, they are very expensive, generally unwieldy, AC wall powered and require the patient to remain immobile in a lying position for greater than 2 hrs per day. CGS are convenient but are only effective in a minority of subjects and are often poorly tolerated. Therefore there is a clinical need to develop an effective treatment of PTS.
Pneumatic compression pumps applied for the treatment of PTS sequentially inflate and deflate air pockets within a sleeve secured over the calf in a wavelike manner, with the wave motion displacing fluid and soft tissue proximally toward the heart. The area of the calf affected by this treatment is the bulky soft tissue at the back of the calf. The large unwieldy size and power of these pneumatic compression systems is due to the inefficiency of the several energy conversion steps in this process. First AC power is turned into the mechanical work of activating a motor which compresses air. The compressed air is then routed through valves to a sleeve with several air pockets. These air pockets are then filled and voided to create the peristaltic like pumping effect on the soft tissues of the calf. Efforts to miniaturize such a system and reduce power levels so that such a device can be worn portably and operated on battery power have not been successful. The result is too little pumping to affect a reasonable result. An innovative alternative uses the walking motion of a subject to compress a working fluid under the sole of the foot which is then routed to the calf, however such a system has no effect when the subject is standing still or sitting.
Deep Vein Thrombosis (DVT) prophylaxis is achieved either by anticoagulants or physical methods. Anticoagulants have side effects, among them increased risk of internal bleeding, which makes them undesirable for some applications, and particularly following major orthopaedic surgery. Of the physical methods, pneumatic compression pumps (devices that pump blood from the calf veins towards the heart) are the most successful and graduated compression hose significantly less so. There is now good evidence that prophylaxis for venous thrombosis should be continued after hospital discharge, because patients remain at risk for up to 6 weeks. Continuing post-discharge prophylaxis is possible with anticoagulants, but not with the available calf compression devices, since the latter are large, unwieldy, need an AC power source, and therefore cannot be used when patients are ambulant. The peristaltic wave-generating device described above is the only wearable ambulatory pump that can achieve DVT prophylaxis comparable to pneumatic compression devices and anticoagulants; hence there is a significant clinical need and advantage to the use of this device
It would therefore be advantageous to provide a compact wave generating device that can be used for producing wave motion for use in chairs, beds or other therapeutic devices.